The present invention relates to a display unit.
Display units have been proposed that use a transmissive liquid crystal display (LCD) or an organic electroluminescent display. The display units have a high image quality under an environment where lighting intensity is low, such as indoors. However, under an environment where lighting intensity is high, such as outdoors, the image quality deteriorates because the contrast decreases. To prevent the contrast from being deteriorated, the brightness of a backlight is increased with the transmissive liquid crystal display. In the case with the organic electroluminescent display, the brightness of illumination is increased. However, in these cases, the power consumption increases.
To reduce power consumption, a transflective liquid crystal display has been developed that is a combination of a reflective liquid crystal display and a transmissive liquid crystal display. However, in the transflective liquid crystal display, one pixel is used for both a reflective LCD and a transmissive LCD. Thus, as compared to the display units that are exclusively used as a reflective LCD or a transmissive LCD, the performance is reduced.
Japanese Laid-Open Patent Publication No. 10-78582 discloses a display unit 50 that uses an organic electroluminescent display as a backlight (see FIG. 6). The display unit 50 includes an organic electroluminescent display 51 and a liquid crystal display 52. The organic electroluminescent element 51 is formed of a reflective cathode electrode 54, an organic electroluminescent layer 55, and an anode electrode 56, which are formed on a substrate 53. The reflective cathode electrode 54 has light reflectivity, and the anode electrode 56 has light transmittance.
The liquid crystal display 52 includes a pair of transparent substrates 57, 58 and a liquid crystal 59, which is sealed between the substrates 57, 58. A polarization plate 60 is located on the front surface (top surface as viewed in FIG. 6) of the substrate 57, and another polarization plate 61 is located on the rear surface (bottom surface as viewed in FIG. 6) of the substrate 58. A pixel electrode 62, an insulation film 63, and an orientation film 64 are located between the substrate 58 and the liquid crystal 59 along a light output direction. Another orientation film 65, a common electrode 66, a protection film 67, and a color filter 68 are located between the substrate 57 and the liquid crystal 59.
To reduce the size of the display unit 50, the thickness of the display unit 50 is desired to be reduced. However, the conventional liquid crystal display 52 has two substrates (glasses), and the organic electroluminescent display 51 has at least one substrate. Therefore, when the liquid crystal display 52 is simply laid over the organic electroluminescent display 51, the sum of the substrates is at least three. Thus, the display unit 50 could not be made thin and light. Also, the organic electroluminescent display 51 and the liquid crystal display 52 each have two types of electrodes, which are cathode and anode. Therefore, the structure of the display unit 50 is complicated when the organic electroluminescent display 51 and the liquid crystal display 52 are combined.